org.apache.commons.math.transform
Class FastFourierTransformer.RootsOfUnity

java.lang.Object
  org.apache.commons.math.transform.FastFourierTransformer.RootsOfUnity

All Implemented Interfaces:

Serializable

Enclosing class:

FastFourierTransformer

private static class FastFourierTransformer.RootsOfUnity
extends Object
implements Serializable

Computes the n^th roots of unity. A cache of already computed values is maintained.

Field Summary

private boolean	isForward Forward/reverse indicator.
private int	omegaCount Number of roots of unity.
private double[]	omegaImaginaryForward Imaginary part of the roots for forward transform.
private double[]	omegaImaginaryInverse Imaginary part of the roots for reverse transform.
private double[]	omegaReal Real part of the roots.
private static long	serialVersionUID Serializable version id.

Constructor Summary

FastFourierTransformer.RootsOfUnity()
Build an engine for computing then ^th roots of unity

Method Summary

void	computeOmega(int n) Computes the nth roots of unity.
double	getOmegaImaginary(int k) Get the imaginary part of the kth nth root of unity
double	getOmegaReal(int k) Get the real part of the kth nth root of unity
boolean	isForward() Check if computation has been done for forward or reverse transform.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

serialVersionUID

private static final long serialVersionUID

Serializable version id.

See Also:

Constant Field Values

omegaCount

private int omegaCount

Number of roots of unity.

omegaReal

private double[] omegaReal

Real part of the roots.

omegaImaginaryForward

private double[] omegaImaginaryForward

Imaginary part of the roots for forward transform.

omegaImaginaryInverse

private double[] omegaImaginaryInverse

Imaginary part of the roots for reverse transform.

isForward

private boolean isForward

Forward/reverse indicator.

Constructor Detail

FastFourierTransformer.RootsOfUnity

public FastFourierTransformer.RootsOfUnity()

Build an engine for computing then ^th roots of unity

Method Detail

isForward

public boolean isForward()
                  throws IllegalStateException

Check if computation has been done for forward or reverse transform.

Returns:

true if computation has been done for forward transform

Throws:

IllegalStateException - if no roots of unity have been computed yet

computeOmega

public void computeOmega(int n)
                  throws IllegalArgumentException

Computes the n^th roots of unity.

The computed omega[] = { 1, w, w², ... w^(n-1) } where w = exp(-2 π i / n), i = &sqrt;(-1).

Note that n is positive for forward transform and negative for inverse transform.

Parameters:

n - number of roots of unity to compute, positive for forward transform, negative for inverse transform

Throws:

IllegalArgumentException - if n = 0

getOmegaReal

public double getOmegaReal(int k)
                    throws IllegalStateException,
                           IllegalArgumentException

Get the real part of the k^th n^th root of unity

Parameters:

k - index of the n^th root of unity

Returns:

real part of the k^th n^th root of unity

Throws:

IllegalStateException - if no roots of unity have been computed yet

IllegalArgumentException - if k is out of range

getOmegaImaginary

public double getOmegaImaginary(int k)
                         throws IllegalStateException,
                                IllegalArgumentException

Get the imaginary part of the k^th n^th root of unity

Parameters:

k - index of the n^th root of unity

Returns:

imaginary part of the k^th n^th root of unity

Throws:

IllegalStateException - if no roots of unity have been computed yet

IllegalArgumentException - if k is out of range